DDX56 Inhibits Type ? Interferon Signal Transduction And Enhances The Foot-and-mouth Disease Virus Replication

Foot-and-mouth disease virus(FMDV)can cause foot-and-mouth disease(FMD)in cloven-hoofed animals such as sheep,cattle and pigs etc.FMD is an acute and highly contagious disease,which causes huge economic losses to animal husbandry around the world.The innate immunity system of the host,the host first line of defense against viral infections,plays a crucial role in removing pathogens and protecting the body.The host infected with FMDV can induce the innate immune response of the host.At the same time,FMDV can promote the replication of the host by using its own protein to antagonize the host's immune response.DEAD-box RNA helicase(DDX56)is mainly involved in the metabolic process of RNA.It`s reported that DDX56 enhances the replication of WNV and HIV.However,the mechanisms are unclear.Our previous research revealed that human DDX56 inhibited the SeV-triggered IFN-? induction,and porcine DDX56 increased FMDV replication.That suggested a potential role of DDX56 in FMDV infection.In order to exploit the mechanisms that DDX56 inhibited the IFN-? induction,we performed the overexpression assay,which indicated overexpression of DDX56 significantly suppressed IFN-? pathway activation and IFNB1 transcription.Knockdown or delete DDX56 markedly increased the SeV-triggered IFN-? induction,and markedly reduced the replication of VSV.DDX56 interacted with IRF3 in a virus infection-dependent manner.Overexpression of DDX56 suppressed nuclear translocation of IRF3,whereas knockdown or knockout of DDX56 increased the interaction between DDX56 and IRF3 during viral infection.A further study revealed that the overexpression of DDX56 disrupted the IRF3-IOP5 interaction,while knockdown or knockout of DDX56 increased the IRF3-IOP5 interaction during viral infection.It revealed that DDX56 suppressed nuclear translocation of IRF3 via disrupting the IRF3-IOP5 interaction.To identity the key site of DDX56,we constructed several mutants of DDX56,and we further found the D166 site is the key site,which inhibited the innate immune response.To explore the mechanism that porcine DDX56 enhanced FMDV infection,we detected the effect of porcine DDX56 on FMDV replication.We investigated overexpression of porcine DDX56 increased FMDV replication,whereas knockdown of porcine DDX56 had opposite effects.We further found porcine DDX56 inhibited the virus-triggered IFN-? activation and interacted with IRF3.It revealed that porcine DDX56 increased FMDV replication by depressing innate immune response.To investigate the mechanism of porcine DDX56 increasing the replication levels of FMDV,luciferase assayes confirmed that porcine DDX56 cooperated with FMDV VP0,VP1,VP2 and 3A to inhibit activation of IFN-?.Coimmunoprecipitation experiments showed that porcine DDX56 interacted with FMDV VP0,VP1,VP2 and 3A.A further study revealed porcine DDX56 cooperated with FMDV 3A to inhibit the phosphorylation of IRF3.Likewise,the D166 site of porcine DDX56 is essential for increasing FMDV replication..As a summary,we demonstrated that DDX56 acted as a negative regulator of SeV-triggered IFN-? induction by disrupting the interacting between IRF3 and IPO5,which inhibited the nuclear translocation of IRF3.Meanwhile,during FMDV infection,DDX56 interacted with FMDV 3A and cooperated with FMDV 3A to inhibit IFN-? by reducing the phosphorylation of IRF3 and ultimately promote replication of FMDV.This study contributes to complicated molecular mechanisms of virus-triggered type I interferon production and a novel antagonistic mechanisms induced by FMDV,which provides new insight into the molecular mechanisms for the innate immune response and pathogenic mechanism of FMDV.